In this paper,a new pill-box window with arc groove disk is studied for S-band high power klystron.Its main characteristics are long pill-box and periodic grooved window disk.The long pill-box window can decrease the ...In this paper,a new pill-box window with arc groove disk is studied for S-band high power klystron.Its main characteristics are long pill-box and periodic grooved window disk.The long pill-box window can decrease the normal field and relieve the radio frequency loss in high power transmission,and periodic grooved window disk can suppress tangential field multipactor.The Monte Carlo(MC)method is used to build up the simulation model and analyze the increasing tendency of electrons.The simulation results indicate that long-box window with periodic arc grooved window disk can restrain multipactor effectively.Homocentric circular half-camber arc slot is put forward to overcome the disadvantages of periodic straight triangle and strait rectangular.The long pill-box with groove disk window prototype is tested in high power Travelling Wave Resonant Ring(TWRR)and the experimental results show an excellent character of this window.展开更多
With the most advanced Synchronous Radiation Photoelectron Spectrum(SRPS),the emission mechanism of M-type cathodes has been investigated from the perspective of chemical state.Based on the experimental results of SRP...With the most advanced Synchronous Radiation Photoelectron Spectrum(SRPS),the emission mechanism of M-type cathodes has been investigated from the perspective of chemical state.Based on the experimental results of SRPS analysis,a new model of the electron emission mechanism for M-type cathode is discussed.The main topics in this paper include the research status of electron emission mechanism of M-type cathodes;the advantages of SRPS technology;the distribution of oxygen chemical state on the cathode surface and the evolvement of oxygen chemical state during activation process;the relation between barium chemical state and osmium(Os)-coating;surplus barium and its formula;the characteristics of Os,and other noble metal coatings;the relation between film characteristics and emission performance of cathodes,the inhibition effects to the emission for Platinum(Pt)-coated cathode,etc.At the end of this paper,electron emission mechanism of M-type cathode is summarized and foreseen.展开更多
The hybrid-mode dispersion equation of the metal-grating periodic slow-wave structure for a rectangular Cerenkov maser is derived by using the Borgnis function and field-matching methods.An equivalent-circuit model fo...The hybrid-mode dispersion equation of the metal-grating periodic slow-wave structure for a rectangular Cerenkov maser is derived by using the Borgnis function and field-matching methods.An equivalent-circuit model for the taper of the groove depth that matches the smooth waveguide to the metal-grating structure is proposed.By using the equivalentcircuit method,as well as the Ansoft high frequency structure simulator（HFSS） code,an appropriate electromagnetic mode for beam-wave interaction is selected and the equivalent-circuit analysis on the taper is given.The calculated results show that a cumulative reflection coefficient of 0.025 for the beam-wave interaction structure at a working frequency of 78.1 GHz can be reached by designing the exponential taper with a TE z10 rectangular waveguide mode as the input and the desired TE x10 mode as the output.It is worth pointing out that by using the equivalent-circuit method,the complex field-matching problems from the traditional field-theory method for taper design can be avoided,so the taper analysis process is markedly simplified.展开更多
The focusing and the stable transport of an intense elliptic sheet electron beam in a uniform magnetic field are investigated thoroughly by using the macroscopic cold-fluid model and the single-particle orbit theory.T...The focusing and the stable transport of an intense elliptic sheet electron beam in a uniform magnetic field are investigated thoroughly by using the macroscopic cold-fluid model and the single-particle orbit theory.The results indicate that the envelopes and the tilted angles of the sheet electron beam obtained by the two theories are consistent.The single-particle orbit theory is more accurate due to its treatment of the space-charge fields in a rectangular drift tube.The macroscopic cold-fluid model describes the collective transport process in order to provide detailed information about the beam dynamics,such as beam shape,density,and velocity profile.The tilt of the elliptic sheet beam in a uniform magnetic field is carefully studied and demonstrated.The results presented in this paper provide two complete theories for systemically discussing the transport of the sheet beam and are useful for understanding and guiding the practical engineering design of electron optics systems in high power vacuum electronic devices.展开更多
To rapidly and accurately investigate the performance of the dielectric loaded rectangular Cerenkov maser, a simplified nonlinear theory is proposed, in which the variations of wave amplitude and wave phase are determ...To rapidly and accurately investigate the performance of the dielectric loaded rectangular Cerenkov maser, a simplified nonlinear theory is proposed, in which the variations of wave amplitude and wave phase are determined by two coupled first-order differential equations. Through combining with the relativistic equation of motion and adopting the forward wave assumption, the evolutions of the forward wave power, the power growth rate, the axial wave number, the accumulated phase offset, and the information of the particle movement can be obtained in a single-pass calculation. For an illustrative example, this method is used to study the influences of the beam current, the gap distance between the beam and the dielectric surface, and the momentum spread on the forward wave. The variations of the saturated power and the saturation length with the working frequency for the beams with different momentum spreads have also been studied. The result shows that the beam wave interaction is very sensitive to the electron beam state. To further verify this simplified theory, a comparison with the result produced from a rigorous method is also provided, we find that the evolution curves of the forward wave power predicted by the two methods exhibit excellent agreement. In practical applications, the developed theory can be used for the design and analysis of the rectangular Cerenkov maser.展开更多
Periodic dielectric-loaded waveguide is one of the diaphragmatic waveguides. For the excellent mode-selective propagation ability, it is of value for applications in gyrotron-traveling-wave amplifiers （gyro-TWT）, ac...Periodic dielectric-loaded waveguide is one of the diaphragmatic waveguides. For the excellent mode-selective propagation ability, it is of value for applications in gyrotron-traveling-wave amplifiers （gyro-TWT）, accelerators, and other microwave propagation systems. This paper focuses on studying the application of the strong lossy-dielectric- loaded periodic waveguide in millimeter-wave gyro-TWT. It is revealed that due to the lossy property of the dielectric, the energy in the dielectric slots is absorbed effectively and the high order Bloch harmonics induced by the periodicity of the structure are suppressed, which changes the discrete spectrum under losstess condition into a continuous one. As a result, the periodicity of the system is severely suppressed and a mode in the hollow region could be approximated by a fast wave mode in an empty waveguide. These results bring specific guidance for the applications of the lossy dielectric-loaded waveguide in gyro-TWTs and other devices.展开更多
Based on the beam wave synchronous interaction in transverse and longitudinal directions at the same time and starting from Maxwell’s equation and linear Vlasov equation, the beam–wave interaction ‘hot’ dispersion...Based on the beam wave synchronous interaction in transverse and longitudinal directions at the same time and starting from Maxwell’s equation and linear Vlasov equation, the beam–wave interaction ‘hot’ dispersion equation considering both cyclotron resonance and Cherenkov resonance in a staggered double metallic grating traveling wave tube is deduced.Through the reasonable selection for geometric and electrical parameters, the numerical calculation and analysis of the ‘hot’ dispersion equation shows that the beam–wave interaction gain and frequency band with the cyclotron resonance enhancement effect are higher than those with only Cherenkov resonance radiation.展开更多
A three-dimensional model of a dielectric-loaded rectangular Cerenkov maser with a sheet electron beam for the beam-wave interaction is proposed.Based on this model,the hybrid-mode dispersion equation is derived with ...A three-dimensional model of a dielectric-loaded rectangular Cerenkov maser with a sheet electron beam for the beam-wave interaction is proposed.Based on this model,the hybrid-mode dispersion equation is derived with the Borgnis potential function by using the field-matching method.Its approximate solution is obtained under the assumption of a dilute electron beam.By using the Ansoft high frequency structural simulator（HFSS） code,the electromagnetic field distribution in the interaction structure is given.Through numerical calculations,the effects of beam thickness,beam and dielectric-layer gap distance,beam voltage,and current density on the resonant growth rate are analysed in detail.展开更多
A theoretical model is developed for calculating the eigenmodes of the multi-gap resonant cavity. The structure of concern is a kind of ladder-type circuit, offering the advantages of easy fabrication, high characteri...A theoretical model is developed for calculating the eigenmodes of the multi-gap resonant cavity. The structure of concern is a kind of ladder-type circuit, offering the advantages of easy fabrication, high characteristic impedance （R/Q）, and thermal capacity in the millimeter wave to THz regime. The eigenfunction expansion method is used to establish the field expressions for the gaps and the coupling region. Then, the match conditions at the interface are employed, which leads to a group of complicate boundary equations in the form of an infinite series. To facilitate the mathematical treatments and perform a highly efficient calculation, these boundary equations are transformed into the algebraic forms through the matrix representations. Finally, the concise dispersion equation is obtained. The roots of the dispersion equation include both the axial modes in the gaps, which include the fundamental and the high-order modes, and the cavity modes in the coupling region. Extensive numerical results are presented and the behaviors of the multi-gap resonant cavity are examined.展开更多
A linear theory of a rectangular Cerenkov maser （RCM） with a sheet electron beam is developed by using the field- match method. Based on the three-dimensional beam-wave interaction model proposed in this paper, a hy...A linear theory of a rectangular Cerenkov maser （RCM） with a sheet electron beam is developed by using the field- match method. Based on the three-dimensional beam-wave interaction model proposed in this paper, a hybrid-mode dispersion equation and its analytical solution are derived for the RCM. Through numerical calculations, the effects of the beam-grating gap, beam thickness, current density, beam voltage and waveguide width on the linear growth rate axe analysed. Moreover, the performance difference between the RCM with the closed transverse boundary and that with the upper open boundary is compared. The results show that the closed RCM model can avoid the effect of RF radiation on beam-wave interaction, which is more rational for practical applications.展开更多
This paper investigates the diocotron instability of an infinitely wide relativistic sheet electron beam in conducting wMls propagating through a uniform magnetic field by using the macroscopic cold-fluid model theory...This paper investigates the diocotron instability of an infinitely wide relativistic sheet electron beam in conducting wMls propagating through a uniform magnetic field by using the macroscopic cold-fluid model theory. Assuming low- frequency perturbations with long axial wavelengths, the eigenvalue equation and the dispersion relation are acquired for a sheet electron beam with sharp boundary profile and uniform density. The results presented in this paper has developed the use of the macroscopic cold-fluid model theory by extending the parameter of the electron cyclotron frequency ωc to a wider usage range, which is restricted to be much larger than the plasma frequency ωp in the previous research work. Theoretical analyses and numerical calculations indicate that the transport of the sheet electron beam will be completely stabilized by augmenting the normalized beam thickness to a conductor gap larger than a threshold λb, which is greatly dependent on the parameter ωc/ωp. The larger ωc/ωp is, the smaller λb will be needed. Moreover, the system parameters, including the wave number kx of the perturbations and the relativistic mass factor γb, will also influence the growth rate of diocotron instability obviously.展开更多
In order to obtain higher emission performance than that of a traditional M-type cathode, we have developed a new type impregnated dispenser cathode. The new cathode is impregnated with a new active substance with mol...In order to obtain higher emission performance than that of a traditional M-type cathode, we have developed a new type impregnated dispenser cathode. The new cathode is impregnated with a new active substance with molar ratio of 26BaO·29SrO·8Sc2O3 ·7CaO·Al2O3 . This paper introduces the emission performance, surface active material, and work function of the new cathode. At 1100℃B , the DC current density and pulse current density are 30.6±1.0 A/cm2 and 171.6±2.8 A/cm2 , respectively, 2.1 and 5.4 times of that of an M-type cathode. The work function of the new cathode is 1.668± 0.002 eV. High concentration O-Al-Sc-Sr-Ba and O-Al-Sc-Ba are found in the pores and at pore edges, respectively. By comparing the emission performances and surface characteristics of as-polished and as-cleaned cathodes, it is proposed that, the emission around pore ends forms the major part of the total emission for the new cathodes.展开更多
The experimental result of terahertz （THz） coherent transition radiation generated from an ultrashort electron bunching beam is reported. During this experiment, the window for THz transmission from ultrahigh vacuum...The experimental result of terahertz （THz） coherent transition radiation generated from an ultrashort electron bunching beam is reported. During this experiment, the window for THz transmission from ultrahigh vacuum to free air is tested. The compact measurement system which can simultaneously test the THz wave power and frequency is built and proofed. With the help of improved Martin-Puplett interferometer and Kramers-Krong transform, the longitudinal bunch length is measured. The results show that the peak power of THz radiation wave is more than 80 kW, and its radiation frequency is from 0.1 THz to 1.5 THz.展开更多
基金Supported by the Youth Scientific and Technological Innovation Funding
文摘In this paper,a new pill-box window with arc groove disk is studied for S-band high power klystron.Its main characteristics are long pill-box and periodic grooved window disk.The long pill-box window can decrease the normal field and relieve the radio frequency loss in high power transmission,and periodic grooved window disk can suppress tangential field multipactor.The Monte Carlo(MC)method is used to build up the simulation model and analyze the increasing tendency of electrons.The simulation results indicate that long-box window with periodic arc grooved window disk can restrain multipactor effectively.Homocentric circular half-camber arc slot is put forward to overcome the disadvantages of periodic straight triangle and strait rectangular.The long pill-box with groove disk window prototype is tested in high power Travelling Wave Resonant Ring(TWRR)and the experimental results show an excellent character of this window.
基金Supported by the National Natural Science Foundation of China(No.60871053)
文摘With the most advanced Synchronous Radiation Photoelectron Spectrum(SRPS),the emission mechanism of M-type cathodes has been investigated from the perspective of chemical state.Based on the experimental results of SRPS analysis,a new model of the electron emission mechanism for M-type cathode is discussed.The main topics in this paper include the research status of electron emission mechanism of M-type cathodes;the advantages of SRPS technology;the distribution of oxygen chemical state on the cathode surface and the evolvement of oxygen chemical state during activation process;the relation between barium chemical state and osmium(Os)-coating;surplus barium and its formula;the characteristics of Os,and other noble metal coatings;the relation between film characteristics and emission performance of cathodes,the inhibition effects to the emission for Platinum(Pt)-coated cathode,etc.At the end of this paper,electron emission mechanism of M-type cathode is summarized and foreseen.
基金Project supported by the National Natural Science Foundation of China (Grant No. 60801031)
文摘The hybrid-mode dispersion equation of the metal-grating periodic slow-wave structure for a rectangular Cerenkov maser is derived by using the Borgnis function and field-matching methods.An equivalent-circuit model for the taper of the groove depth that matches the smooth waveguide to the metal-grating structure is proposed.By using the equivalentcircuit method,as well as the Ansoft high frequency structure simulator（HFSS） code,an appropriate electromagnetic mode for beam-wave interaction is selected and the equivalent-circuit analysis on the taper is given.The calculated results show that a cumulative reflection coefficient of 0.025 for the beam-wave interaction structure at a working frequency of 78.1 GHz can be reached by designing the exponential taper with a TE z10 rectangular waveguide mode as the input and the desired TE x10 mode as the output.It is worth pointing out that by using the equivalent-circuit method,the complex field-matching problems from the traditional field-theory method for taper design can be avoided,so the taper analysis process is markedly simplified.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60501019,10775139 and 60971073)
文摘The focusing and the stable transport of an intense elliptic sheet electron beam in a uniform magnetic field are investigated thoroughly by using the macroscopic cold-fluid model and the single-particle orbit theory.The results indicate that the envelopes and the tilted angles of the sheet electron beam obtained by the two theories are consistent.The single-particle orbit theory is more accurate due to its treatment of the space-charge fields in a rectangular drift tube.The macroscopic cold-fluid model describes the collective transport process in order to provide detailed information about the beam dynamics,such as beam shape,density,and velocity profile.The tilt of the elliptic sheet beam in a uniform magnetic field is carefully studied and demonstrated.The results presented in this paper provide two complete theories for systemically discussing the transport of the sheet beam and are useful for understanding and guiding the practical engineering design of electron optics systems in high power vacuum electronic devices.
基金Project supported by the National Natural Science Foundation of China (Grant No. 60801031)
文摘To rapidly and accurately investigate the performance of the dielectric loaded rectangular Cerenkov maser, a simplified nonlinear theory is proposed, in which the variations of wave amplitude and wave phase are determined by two coupled first-order differential equations. Through combining with the relativistic equation of motion and adopting the forward wave assumption, the evolutions of the forward wave power, the power growth rate, the axial wave number, the accumulated phase offset, and the information of the particle movement can be obtained in a single-pass calculation. For an illustrative example, this method is used to study the influences of the beam current, the gap distance between the beam and the dielectric surface, and the momentum spread on the forward wave. The variations of the saturated power and the saturation length with the working frequency for the beams with different momentum spreads have also been studied. The result shows that the beam wave interaction is very sensitive to the electron beam state. To further verify this simplified theory, a comparison with the result produced from a rigorous method is also provided, we find that the evolution curves of the forward wave power predicted by the two methods exhibit excellent agreement. In practical applications, the developed theory can be used for the design and analysis of the rectangular Cerenkov maser.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60871051,60871047 and 60971072)
文摘Periodic dielectric-loaded waveguide is one of the diaphragmatic waveguides. For the excellent mode-selective propagation ability, it is of value for applications in gyrotron-traveling-wave amplifiers （gyro-TWT）, accelerators, and other microwave propagation systems. This paper focuses on studying the application of the strong lossy-dielectric- loaded periodic waveguide in millimeter-wave gyro-TWT. It is revealed that due to the lossy property of the dielectric, the energy in the dielectric slots is absorbed effectively and the high order Bloch harmonics induced by the periodicity of the structure are suppressed, which changes the discrete spectrum under losstess condition into a continuous one. As a result, the periodicity of the system is severely suppressed and a mode in the hollow region could be approximated by a fast wave mode in an empty waveguide. These results bring specific guidance for the applications of the lossy dielectric-loaded waveguide in gyro-TWTs and other devices.
基金supported by National Natural Science Foundation of China(No.61671431)
文摘Based on the beam wave synchronous interaction in transverse and longitudinal directions at the same time and starting from Maxwell’s equation and linear Vlasov equation, the beam–wave interaction ‘hot’ dispersion equation considering both cyclotron resonance and Cherenkov resonance in a staggered double metallic grating traveling wave tube is deduced.Through the reasonable selection for geometric and electrical parameters, the numerical calculation and analysis of the ‘hot’ dispersion equation shows that the beam–wave interaction gain and frequency band with the cyclotron resonance enhancement effect are higher than those with only Cherenkov resonance radiation.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60801031 and 10905032)the Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No. YYYJ-1123-5)
文摘A three-dimensional model of a dielectric-loaded rectangular Cerenkov maser with a sheet electron beam for the beam-wave interaction is proposed.Based on this model,the hybrid-mode dispersion equation is derived with the Borgnis potential function by using the field-matching method.Its approximate solution is obtained under the assumption of a dilute electron beam.By using the Ansoft high frequency structural simulator（HFSS） code,the electromagnetic field distribution in the interaction structure is given.Through numerical calculations,the effects of beam thickness,beam and dielectric-layer gap distance,beam voltage,and current density on the resonant growth rate are analysed in detail.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61222110 and 60971073)
文摘A theoretical model is developed for calculating the eigenmodes of the multi-gap resonant cavity. The structure of concern is a kind of ladder-type circuit, offering the advantages of easy fabrication, high characteristic impedance （R/Q）, and thermal capacity in the millimeter wave to THz regime. The eigenfunction expansion method is used to establish the field expressions for the gaps and the coupling region. Then, the match conditions at the interface are employed, which leads to a group of complicate boundary equations in the form of an infinite series. To facilitate the mathematical treatments and perform a highly efficient calculation, these boundary equations are transformed into the algebraic forms through the matrix representations. Finally, the concise dispersion equation is obtained. The roots of the dispersion equation include both the axial modes in the gaps, which include the fundamental and the high-order modes, and the cavity modes in the coupling region. Extensive numerical results are presented and the behaviors of the multi-gap resonant cavity are examined.
基金supported by the National Natural Science Foundation of China (Grant No. 60801031)
文摘A linear theory of a rectangular Cerenkov maser （RCM） with a sheet electron beam is developed by using the field- match method. Based on the three-dimensional beam-wave interaction model proposed in this paper, a hybrid-mode dispersion equation and its analytical solution are derived for the RCM. Through numerical calculations, the effects of the beam-grating gap, beam thickness, current density, beam voltage and waveguide width on the linear growth rate axe analysed. Moreover, the performance difference between the RCM with the closed transverse boundary and that with the upper open boundary is compared. The results show that the closed RCM model can avoid the effect of RF radiation on beam-wave interaction, which is more rational for practical applications.
基金supported by the National Natural Science Foundation of China (Grant Nos. 60501019, 10775139, and 60971073)
文摘This paper investigates the diocotron instability of an infinitely wide relativistic sheet electron beam in conducting wMls propagating through a uniform magnetic field by using the macroscopic cold-fluid model theory. Assuming low- frequency perturbations with long axial wavelengths, the eigenvalue equation and the dispersion relation are acquired for a sheet electron beam with sharp boundary profile and uniform density. The results presented in this paper has developed the use of the macroscopic cold-fluid model theory by extending the parameter of the electron cyclotron frequency ωc to a wider usage range, which is restricted to be much larger than the plasma frequency ωp in the previous research work. Theoretical analyses and numerical calculations indicate that the transport of the sheet electron beam will be completely stabilized by augmenting the normalized beam thickness to a conductor gap larger than a threshold λb, which is greatly dependent on the parameter ωc/ωp. The larger ωc/ωp is, the smaller λb will be needed. Moreover, the system parameters, including the wave number kx of the perturbations and the relativistic mass factor γb, will also influence the growth rate of diocotron instability obviously.
基金Supported by the National Natural Science Foundation of China (No. 60871053)the Major State Basic Research Development Program of China (No. 2013CB328901)
文摘In order to obtain higher emission performance than that of a traditional M-type cathode, we have developed a new type impregnated dispenser cathode. The new cathode is impregnated with a new active substance with molar ratio of 26BaO·29SrO·8Sc2O3 ·7CaO·Al2O3 . This paper introduces the emission performance, surface active material, and work function of the new cathode. At 1100℃B , the DC current density and pulse current density are 30.6±1.0 A/cm2 and 171.6±2.8 A/cm2 , respectively, 2.1 and 5.4 times of that of an M-type cathode. The work function of the new cathode is 1.668± 0.002 eV. High concentration O-Al-Sc-Sr-Ba and O-Al-Sc-Ba are found in the pores and at pore edges, respectively. By comparing the emission performances and surface characteristics of as-polished and as-cleaned cathodes, it is proposed that, the emission around pore ends forms the major part of the total emission for the new cathodes.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.10905032 and 10975088)China Postdoctoral Science Foundation (Grant No.20080440031)the China Postdoctoral Special Science Foundation (Grant No.200902088)
文摘The experimental result of terahertz （THz） coherent transition radiation generated from an ultrashort electron bunching beam is reported. During this experiment, the window for THz transmission from ultrahigh vacuum to free air is tested. The compact measurement system which can simultaneously test the THz wave power and frequency is built and proofed. With the help of improved Martin-Puplett interferometer and Kramers-Krong transform, the longitudinal bunch length is measured. The results show that the peak power of THz radiation wave is more than 80 kW, and its radiation frequency is from 0.1 THz to 1.5 THz.
